Thermodynamics is a science concerned with relations between work and heat. Virtually every chemical reaction or physiological process in animals or cells occurs with the absorption or generation of heat and thus, any heat absorbed or generated by a system is proportional to the amount of work done. Consequently, measurement of heat output (i.e., thermogenesis) can be used to estimate the energy used in or produced by chemical reactions and physiological processes.
Various methods (e.g., Northern or Western-blotting) are available for detecting the expression of proteins that regulate thermogenesis in cells (e.g., uncoupling proteins, UCPs), but these methods are labor intensive and do not directly measure protein activity. Guanosine 5′-diphosphate (GDP)-binding assays and fluorescent dyes (e.g., JC-1 or rhodamine derivatives) provide a direct measure of UCP activity (Nedergaard and Cannon, Am. J. Physiol. 248(3 Pt 1):C365-C371 (1985); (Reers et al, Biochemistry 30:4480-4486 (1991)). However, GDP-binding assays require protein purification and use of dyes is limited because of non-selective staining, cytotoxicity, and metabolism of the dyes by cells. More importantly, all of these techniques fail to directly measure real-time fluctuations in thermogenesis and are invasive.
Bomb calorimeters and microcalorimeters provide a means for quantitatively measuring the heat generated or consumed by cultured cells (Bottcher and Furst, J. Biochem. Biophys. Methods 32: 191-194 (1996)) or chemical reactions. However, despite recent progress in developing multichannel calorimeters, methods for rapidly analyzing changes in heat in multiple simultaneous reactions (≧60) are not available. Moreover, temperature gradations over fixed surface areas, such as those in cell culture plates or on the surface of skin, cannot be measured using calorimeters.
Infrared thermometers have been developed that can measure the magnitude of infrared energy emitted from a specific body site (e.g., the ear canal). These instruments, however, cannot be used to measure heat production of isolated cells, tissues, or chemical reactions and cannot provide real time measurements of heat output by multiple samples over extended periods of time. Moreover, these devices do not provide images over large surface areas.
Infrared interactance instruments have also been developed. Unlike infrared thermometers, these instruments contain diodes that emit near radiation at wavelengths of <1000 nm. Since these instruments measure the absorption of near infrared radiation, they do not provide an accurate measure of thermogenesis.
The present invention provides a rapid non-invasive method of measuring real-time thermogenesis in animals, plants, tissues and isolated cells, including cells in culture. This invention extends to molecular interactions, such as receptor-ligand binding, enzyme catalysis, and other chemical reactions that alter heat output. The present method, which is based on the use of infrared thermography, can be used to screen and identify drug candidates for treating various diseases, disorders and conditions. Additionally, the present method can be used to visualize thermal changes within an animal tissue or organ, which can have significant uses in monitoring various effects and reactions within a subject.
Body shape and metabolic changes associated with the use of retroviral therapies are causing increasing concern among physicians who treat patients with HIV/AIDS. These changes in metabolism are due to a lipodystrophy syndrome which is characterized by an increase in abdominal fat and loss of subcutaneous adipose depots (Carr A., et al. Lancet 353, 2093-2099 (1999)). The present method can also advantageously be used to diagnose lipodystrophy in a patient, in particular, well before pathophysiological data typically becomes available. Such a diagnostic would allow treatment at an earlier stage in progression of the syndrome.